The epidermal growth factor receptor (EGFR) is a member of epidermal growth factor gene (erbB) family, and has significant influence in the development of various cancers, such as breast cancer, colon cancer, head and neck tumor, renal cancer, lung cancer, pancreatic cancer, prostatic cancer. Many domestic and overseas studies showed that the antibody against EGFR can inhibit EGFR signal transduction pathway by effectively blocking extracellular ligand binding, and has good therapeutic effect on human tumors expressed by various EGFR, especially head and neck squamous cell carcinoma (80%-100%), colorectal cancer (25%-77%), non-small-cell lung cancer (40%-80%) and pancreatic cancer. Currently, the epidermal growth factor receptor is one of deeply-studied and greatly-concerned tumor therapeutic targets, and it is one of research hotspots of current tumor treatment to use genetic engineering means to develop anti-EGFR monoclonal antibody.
At present, two anti-EGFR therapeutic antibodies have been approved by American FDA, viz. anti-EGFR mouse-human chimeric antibody Cetuximab (trade name: Erbitux) and anti-EGFR fully human antibody Panitumumab respectively, which are all used for the treatment of colorectal cancer and head and neck tumor. In 2005, anti-EGFR human antibody Nimotuzumab (trade name: TAIXINSHENG) was granted a new medicine certificate of Class 1 by Chinese Food and Drug Administration (CFDA). The antibody against the target being developed comprises human monoclonal antibody Pertuzumab, human antibodies Zalutumumab and Necitumumab, etc. Although the antigen epitopes to which they bind are different, they all can play a role in inhibiting biological functions mediated by EGFR.
Human antibody is the final development direction of a therapeutic antibody, and the use of human antibody in clinic can maximally reduce the immunogenicity of the antibody, prolong the half-life period of the antibody in vivo, and mediate immune regulation, ADCC and CDC effection by means of human immunoglobulin Fc fragment, and thereby enhance the biological effect of the antibody. The main means for development of the human antibody comprises antibody library technology and transgenic mouse technology. Currently, the large-capacity antibody library technology is well-established, especially the phage display antibody library technology has successfully made several fully human antibodies be sold on the market. In a constructed large-capacity antibody library, the semisynthetic antibody library of CAT company and fully synthetic antibody library of Marphosys AG company are the most representative and most successful examples. In particular, tens of candidate antibodies with development value have been obtained through the HuCAL GOLD technology of Marphosys AG company, and now there has been 17 projects entering clinical stage. The greatest advantage of such a technology is that it can optimize the antibody library via reasonable design, and the antibody framework gene thereof is a replaceable box structure, facilitating later optimization and modification of the antibody. Based on such an advantage, the HuCAL library so far has updated the antibody library thereof to third generation, of which the library capacity reaches 4.5×1010, and from which high-affinity antibody with affinity up to pM level can be screened. Therefore, technologically, the use of antibody library technology to obtain therapeutic human antibody is well-established today, and is considered as one of the current most successful technical means for developing a therapeutic antibody. Through technology optimization and exploration, the applicant invented a high-effective method for DNA linkage and conversion, and applied it to construction of large-capacity phage antibody library. A large-capacity fully synthetic phage single chain human antibody resource library with library capacity up to 1.35×1010 (ZL.200910091261.8) has been constructed, and multiple specific antibodies against different targets have been screened from the antibody library. The antibody Ame55 of the present invention is screened and obtained from the antibody library.